Methods and apparatus for creating a downhole buoyant casing chamber

Abstract

Methods and apparatus for creating a downhole buoyant casing chamber. The buoyant casing chamber may be created after the casing has been at least partially run into the wellbore. Some embodiments also allow circulation of fluid as the casing is being run after the creation of the buoyant chamber. A method of the invention comprises running a length of casing into the well to a first step, forming a buoyant chamber in the casing, filling the chamber with buoyant fluid, either a gas or a light liquid, and running the casing to a second depth greater than the first depth. The apparatus used comprises a length of casing, a floating device disposed in a lower end of the casing and forming a lower boundary of a buoyant chamber, a packer for sealingly engaging the casing in an upper end of the buoyant chamber, and a volume of buoyant fluid to fill the chamber.

What is claimed is:  
     
       1. A method of installing casing in a well comprising the steps of: 
       (a) running a length of casing having a floating device adjacent to a lower end thereof into the well to a first depth;  
       (b) forming a buoyant chamber in the casing, comprising:  
       positioning tubing in the casing above the floating device, the tubing having a subsurface release plug on a lower end thereof and having a packer thereon above the plug; and  
       actuating the packer into sealing engagement with the casing thereby forming the buoyant chamber between the packer and plug;  
       (c) filling the chamber with a buoyant fluid; and  
       (d) running the casing to a second depth greater than the first depth.  
     
     
       2. The method of  claim 1  further comprising: 
       during step (d), circulating fluid through the tubing.  
     
     
       3. The method of  claim 2  further comprising: 
       (e) placing the tubing in communication with a portion of the well casing below the plug.  
     
     
       4. The method of  claim 3  wherein step (e) comprises actuating a sleeve by applying pressure thereto such that a port defined in the sleeve is opened. 
     
     
       5. The method of  claim 1  wherein the buoyant fluid is gas selected from the group consisting of nitrogen, air and carbon dioxide. 
     
     
       6. The method of  claim 1  wherein the buoyant fluid is a liquid selected from the group consisting of diesel fuel and water. 
     
     
       7. A method of installing casing in a well comprising the steps of 
       (a) forming a buoyant chamber in a length of casing having a floating device adjacent to a lower end thereof, comprising:  
       positioning tubing in the casing above the floating device, the tubing having a subsurface release plug on a lower end thereof and having a packer thereon above the plug; and  
       actuating the packer into sealing engagement with the casing thereby forming the buoyant chamber between the packer and plug;  
       (b) running the casing into the well to a desired depth; and  
       (c) during step (b), circulating fluid through the casing.  
     
     
       8. The method of  claim 7  wherein: 
       step (c) comprises circulating fluid through the tubing.  
     
     
       9. The method of  claim 7  further comprising: 
       (d) placing the tubing in communication with a portion of the well casing below the plug.  
     
     
       10. The method of  claim 9  wherein step (d) comprises actuating a sleeve by applying pressure thereto such that a port defined in the sleeve is opened. 
     
     
       11. An apparatus for forming a buoyant chamber in a well casing, the apparatus comprising: 
       a length of the casing;  
       a floating device disposed in a lower end of the casing and forming a lower boundary of the buoyant chamber;  
       sealing means for sealingly engaging the casing at an upper end of the buoyant chamber, the sealing means comprising a packer forming an upper boundary of the buoyant chamber when in sealing engagement with the casing;  
       a volume of buoyant fluid to fill the buoyant chamber;  
       tubing extending through the packer whereby the packer is positioned in the casing;  
       a flow path below the packer through which the buoyant fluid may be injected into the buoyant chamber; and  
       a plug below the flow path and connected to a lower end of the tubing, the plug and tubing being adapted for moving downwardly in the buoyant chamber such that the plug is engaged with the floating device as the gas is injected into the buoyant chamber above the plug.  
     
     
       12. The apparatus of  claim 11 , further comprising: 
       a rupture disk initially disposed in the flow path and adapted for rupturing at a predetermined pressure, thereby placing the tubing and buoyant chamber in communication.  
     
     
       13. The apparatus of  claim 11  further comprising a sleeve defining a sleeve port therein, the sleeve being disposed in the plug and having an initially closed position and being movable to an open position, after the plug is engaged with the floating device, such that the tubing is placed in communication with the floating device. 
     
     
       14. The apparatus of  claim 13  wherein the sleeve is moved by a ball dropped down the tubing and pressure applied thereto. 
     
     
       15. The apparatus of  claim 14  wherein the sleeve further defines a chamber port therein; and 
       further comprising a rupture disk in the chamber port adapted for rupturing at a predetermined pressure after the ball has been dropped, thereby placing the tubing and buoyant chamber in communication.  
     
     
       16. method of installing casing in a well comprising the steps of: 
       (a) running a length of casing having a floating device adjacent to a lower end thereof into the well to a first depth;  
       (b) forming a buoyant chamber in the casing, comprising:  
       positioning tubing in the casing above the floating device, the tubing having a subsurface release plug on a lower end thereof and having a packer thereon above the plug; and  
       actuating the packer into sealing engagement with the casing;  
       (c) filling the chamber with a buoyant fluid, comprising injecting the buoyant fluid above the plug, thereby moving the plug and tubing downwardly such that the plug is placed into engagement with the floating device; and  
       (d) running the casing to a second depth greater than the first depth.  
     
     
       17. The method of  claim 16  wherein step (c) comprises: 
       rupturing a rupture disc in communication with the tubing so that the buoyant fluid may be injected above the plug.  
     
     
       18. The method of  claim 16  further comprising: 
       disconnecting the tubing from the packer at a location thereabove.  
     
     
       19. A method of installing casing in a well comprising the steps of: 
       (a) forming a buoyant chamber in a length of casing having a floating device adjacent to a lower end thereof, comprising:  
       positioning tubing in the casing above the floating device, the tubing having a subsurface release plug on a lower end thereof and having a packer thereon above the plug:  
       actuating the packer into sealing engagement with the casing; and  
       injecting the buoyant fluid above the plug, thereby moving the plug and tubing downwardly such that the plug is placed into engagement with the floating device;  
       (b) running the casing into the well to a desired depth; and  
       (c) during step (b), circulating fluid through the casing.  
     
     
       20. The method of  claim 19  wherein step (a) comprises: 
       rupturing a rupture disc in communication with the tubing so that the buoyant fluid may be injected above the plug.  
     
     
       21. The method of  claim 19  further comprising: 
       disconnecting the tubing from the packer at a location above the packer.